Water resistant aluminum pigment dispersion, aqueous ink composition containing the same, and method for manufacturing water resistant aluminum pigment dispersion

ABSTRACT

A water resistant aluminum pigment dispersion includes a water resistant aluminum pigment which is an aluminum pigment covered with a silica film, wherein the water resistant aluminum pigment is formed of an aluminum pigment having an average thickness from 5 nm to 30 nm and a covering film which contains Si and is formed on the surface of the aluminum pigment; and wherein the coverage ratio of the surface of the aluminum pigment by the covering film, calculated from the composition ratio of C, O, Al, and Si detected by XPS measurement at an incident angle of 30°, is in a range from 30% to 90%.

BACKGROUND

1. Technical Field

The present invention relates to a water resistant aluminum pigmentdispersion, an aqueous ink composition containing the same, and a methodfor manufacturing a water resistant aluminum pigment dispersion.

2. Related Art

Heretofore, as a method for forming a coating film having a metallicgloss on a printed material, for example, a method using a printing inkin which a gold powder or a silver powder formed, for example, from abrass or an aluminum fine powder is contained as a pigment, a foil pressprinting method using a metal foil, or a thermal transfer method using ametal foil may be mentioned.

In recent years, many applications of ink jet techniques have beenperformed in printing fields, and as one of the applications, metallicprinting may be mentioned, so that development of an ink having ametallic gloss has been carried out. For example, in JP-A-2008-174712,an aluminum pigment dispersion containing an organic solvent, such as analkylene glycol, as a basic component and a non-aqueous ink compositioncontaining the above dispersion have been disclosed.

On the other hand, in views of global environmental conservation, safetyfor human beings, and the like, instead of a non-aqueous ink compositioncontaining an organic solvent as a basic component, development of anaqueous ink composition has been actually desired. However, when analuminum pigment is dispersed in water, it generates a hydrogen gas andalso forms alumina by a reaction with water, and whitening occursthereby. As a result, in the aluminum pigment, its metallic gloss may bedisadvantageously degraded in some cases.

Accordingly, for example, in JP-A-2004-131542, a technique has beendisclosed in which after the surface of an aluminum pigment is coveredwith a hydrolysis-condensation product containing a siloxane bond, thealuminum pigment is dispersed in water or an aqueous solvent containinga surfactant.

However, when an aluminum pigment provided with siloxane bonds on thesurface thereof is dispersed in an aqueous solvent, particles of thealuminum pigment may agglomerate with each other, and/or a metallicgloss of the aluminum pigment may be degraded in some cases due to theagglomeration.

SUMMARY

An advantage of some aspects of the invention is to provide a waterresistant aluminum pigment dispersion which prevents whitening whenblended with an aqueous paint or an aqueous ink composition and whichhas superior water dispersibility and metallic gloss.

The invention can be realized as the following embodiments orapplication examples.

APPLICATION EXAMPLE 1

According to one aspect of the invention, there is provided a waterresistant aluminum pigment dispersion including a water resistantaluminum pigment which is an aluminum pigment covered with a silicafilm, and in this water resistant aluminum pigment dispersion, the waterresistant aluminum pigment is dispersed in an aqueous solutioncontaining at least one selected from the group consisting of acopolymer A including a structural unit represented by the followinggeneral formula (1) or the following formula (2) and a structural unitrepresented by the following general formula (3), a copolymer Bincluding a structural unit represented by the following general formula(1) or the following formula (2) and a structural unit represented bythe following general formula (4), and a copolymer C including astructural unit represented by the following general formula (1) or thefollowing formula (2) and a structural unit represented by the generalformula (5).

In the formula, A₁ and A₂ each independently indicate hydrogen, analkali metal, or ammonium.

In the formula, m indicates an integer of 1 to 5.

In the formula, n indicates an integer of 1 to 5.

In the formula, o indicates an integer of 1 to 5, and R indicates analkyl group.

According to the water resistant aluminum pigment dispersion ofApplication Example 1, since the silica film is formed on the surface ofthe aluminum pigment, a water resistance is imparted thereto, and evenwhen the aluminum pigment is blended with an aqueous paint or an aqueousink composition, the metallic gloss is not degraded. In addition, sincethe aluminum pigment covered with the silica film is dispersed in anaqueous solution containing at least one selected from the groupconsisting of the copolymer A, the copolymer B, and the copolymer C, awater resistant aluminum pigment dispersion having superior waterdispersibility can be obtained without degrading the water resistanceand the metallic gloss.

APPLICATION EXAMPLE 2

According to Application Example 1, the aluminum pigment may includeplate-shaped particles having an average thickness of 5 to 30 nm and a50% average particle diameter of 0.5 to 3 μm.

APPLICATION EXAMPLE 3

According to Application Example 1 or 2, the silica film may have athickness of 0.5 to 10 nm.

APPLICATION EXAMPLE 4

According to one of Application Examples 1 to 3, the water resistantaluminum pigment may be the aluminum pigment processed by a surfacetreatment using tetraethoxysilane.

APPLICATION EXAMPLE 5

According to one of Application Examples 1 to 4, the copolymer A, thecopolymer B, and the copolymer C each may have a weight averagemolecular weight of 2000 to 500,000.

APPLICATION EXAMPLE 6

According to one of Application Examples 1 to 5, the total of thecontents of the copolymer A, the copolymer B, and the copolymer C may be0.02 to 1.5 parts by mass with respect to 1 part by mass of the aluminumpigment.

APPLICATION EXAMPLE 7

According to another aspect of the invention, there is provided anaqueous ink composition which comprises the water resistant aluminumpigment dispersion according to one of Application Examples 1 to 6.

APPLICATION EXAMPLE 8

According to another aspect of the invention, there is provided a methodfor manufacturing a water resistant aluminum pigment dispersioncomprising: a first step of adding tetraethoxysilane to an aluminumpigment dispersion in which an aluminum pigment is dispersed in anorganic solvent to form a silica film on the surface of the aluminumpigment by a reaction between a hydroxyl group present on the surface ofthe aluminum pigment and the tetraethoxysilane; a second step ofremoving at least part of the organic solvent; and a third step ofadding an aqueous surfactant solution.

According to the water resistant aluminum pigment dispersion ofApplication Example 8, since the silica film is formed on the surface ofthe aluminum pigment, a water resistance is imparted thereto, and evenwhen the aluminum pigment is blended with an aqueous paint or an aqueousink composition, the metallic gloss is not degraded. In addition, sincethe aluminum pigment covered with the silica film is dispersed in theaqueous surfactant solution, a water resistant aluminum pigmentdispersion having superior water dispersibility can be obtained withoutdegrading the water resistance and the metallic gloss.

APPLICATION EXAMPLE 9

According to Application Example 8, the surfactant may be at least oneof a polycarboxylic acid and a salt thereof.

APPLICATION EXAMPLE 10

According to Application Example 9, the polycarboxylic acid and the saltthereof may be at least one selected from the group consisting of acopolymer A including a structural unit represented by the followinggeneral formula (1) or the following formula (2) and a structural unitrepresented by the following general formula (3), a copolymer Bincluding a structural unit represented by the following general formula(1) or the following formula (2) and a structural unit represented bythe following general formula (4), and a copolymer C including astructural unit represented by the following general formula (1) or thefollowing formula (2) and a structural unit represented by the generalformula (5).

In the formula, A₁ and A₂ each independently indicate hydrogen, analkali metal, or ammonium.

In the formula, m indicates an integer of 1 to 5.

In the formula, n indicates an integer of 1 to 5.

In the formula, o indicates an integer of 1 to 5, and R indicates analkyl group.

APPLICATION EXAMPLE 11

According to one of Application Examples 8 to 10, the first step, thesecond step, and the third step may be performed in that order.

APPLICATION EXAMPLE 12

According to one of Application Examples 8 to 11, the aluminum pigmentmay include plate-shaped particles having an average thickness of 5 to30 nm and a 50% average particle diameter of 0.5 to 3 μm.

APPLICATION EXAMPLE 13

According to one of Application Examples 8 to 12, the silica film mayhave a thickness of 0.5 to 10 nm.

APPLICATION EXAMPLE 14

According to one of Application Examples 10 to 13, the copolymer A, thecopolymer B, and the copolymer C each may have a weight averagemolecular weight of 200 to 500,000.

APPLICATION EXAMPLE 15

According to one of Application Examples 8 to 14, the addition amount ofthe surfactant may be 0.02 to 1.5 parts by mass with respect to 1 partby mass of the aluminum pigment.

APPLICATION EXAMPLE 16

According to one of Application Examples 8 to 15, the organic solventmay include diethylene glycol diethyl ether.

APPLICATION EXAMPLE 17

According to one of Application Examples 8 to 16, in the first step,ammonia may be added.

APPLICATION EXAMPLE 18

According to one of Application Examples of 8 to 17, in the second step,the aluminum pigment provided with the silica film may be separated fromthe organic solvent by centrifugal separation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIGS. 1A and 1B are views each schematically showing a photoelectrontakeoff angle in XPS measurement.

FIG. 2 is a SEM image showing a surface condition of a water resistantaluminum pigment in a water resistant aluminum pigment dispersion ofthis embodiment.

FIG. 3 is a TEM image showing a cross-sectional condition of the waterresistant aluminum pigment in the water resistant aluminum pigmentdispersion of this embodiment.

FIG. 4 is a TEM image showing a cross-sectional condition of the waterresistant aluminum pigment in the water resistant aluminum pigmentdispersion of this embodiment.

FIG. 5 is a TEM image showing a cross-sectional condition of the waterresistant aluminum pigment in the water resistant aluminum pigmentdispersion of this embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferable embodiments of the invention will be described.The embodiments described below are examples for explaining theinvention. In addition, the invention is not limited to the followingembodiments and also includes various modified examples performedwithout departing from the scope of the invention.

1. Method for Manufacturing Water Resistant Aluminum Pigment Dispersion

A method for manufacturing a water resistant aluminum pigment dispersionaccording to one embodiment of the invention comprises a first step ofadding tetraethoxysilane to an aluminum pigment dispersion in which analuminum pigment is dispersed in an organic solvent to form a silicafilm on the surface of the aluminum pigment by a reaction between ahydroxyl group present on the surface of the aluminum pigment and thetetraethoxysilane; a second step of removing at least part of theorganic solvent; and a third step of adding an aqueous surfactantsolution.

Hereinafter, the above individual steps will be described in detail.

1.1 First Step

First, by the following steps (1) and (2), an aluminum pigmentdispersion in which an aluminum pigment is dispersed in an organicsolvent is prepared.

(1) A composite pigment base is prepared which has the structure inwhich a peeling resin layer and an aluminum or an aluminum alloy layer(hereinafter simply referred to as “aluminum layer”) are sequentiallylaminated on a sheet-shaped substrate.

Although the sheet-shaped substrate is not particularly limited, forexample, there may be mentioned a mold releasing film, such as apolyolefin film of a poly(tetrafluoroethylene), a polyethylene, apolypropylene, or the like, a polyester film of a poly(ethyleneterephthalate) or the like, a polyamide film of a nylon 66, a nylon 6,or the like, a polycarbonate film, a triacetate film, or a polyimidefilm. Among those mentioned above, a film of a poly(ethyleneterephthalate) or a copolymer thereof is preferable.

Although the thickness of the sheet-shaped substrate is not particularlylimited, it is preferably in the range of 10 to 150 μm. When thethickness is 10 μm or more, handling of the substrate in the steps orthe like may not cause any problems, and when the thickness is 150 μm orless, since having sufficient flexibility, the substrate may be, forexample, rolled up or peeled away without causing any problems.

The peeling resin layer is an undercoat layer for the aluminum layer andis also a peeling promotion layer to promote the peeling from thesheet-shaped substrate. As a resin used for this peeling resin layer,for example, a poly(vinyl alcohol), a poly(vinyl butyral), apoly(ethylene glycol), a poly(acrylic acid), a poly(acryl amide), acellulose derivative, or a modified nylon resin is preferable.

When a solution containing at least one of the resins mentioned above byway of example is applied to the sheet-shaped substrate and is thendried, the peeling resin layer can be formed. After the application, anadditive, such as a viscosity modifier, may also be added.

The application of the peeling resin layer may be performed by a knowntechnique, such as gravure application, roll application, bladeapplication, extrusion application, dip application, or spin coatapplication, which has been generally used. After the application anddrying, whenever necessary, the surface may be smoothed by a calenderingtreatment.

Although the thickness of the peeling resin layer is not particularlylimited, it is preferably in the range of 0.5 and 50 μm and morepreferably in the range of 1 and 10 μm. When the thickness is less than0.5 μm, the amount is not sufficient as a dispersing resin, and when thethickness is more than 50 μm, peeling is liable to occur at theinterface with the pigment layer when being rolled up therewith.

As a method for laminating the aluminum layer, a vacuum deposition, anion plating, or a sputtering method is preferably used.

In addition, as exemplified in JP-A-2005-68250, the aluminum layer maybe sandwiched by protective layers. As the protective layer, forexample, a silicon oxide layer or a protective resin layer may bementioned.

The silicon oxide layer is not particularly limited as long as itcontains silicon oxide but is preferably formed by a sol-gel method froma silicon alkoxide, such as a tetraalkoxysilane, or a polymer thereof.When an alcohol solution dissolving a silicon alkoxide or a polymerthereof is applied and is then fired by heating, a coating film of asilicon oxide layer is formed.

For the protective resin layer, any resin may be used as long as it isnot dissolved in a dispersion medium, and for example, a poly(vinylalcohol), a poly(ethylene glycol), a poly(acrylic acid), a poly(acrylamide), or a cellulose derivative may be mentioned. Among thosementioned above, a poly(vinyl alcohol) or a cellulose derivative ispreferably used.

When an aqueous solution containing at least one of the resins mentionedabove by way of example is applied and is then dried, the protectiveresin layer can be formed. After the application, an additive, such as aviscosity modifier, may be added. The application of the silicon oxideand the resin is performed by a method similar to that for theapplication of the peeling resin layer.

The thickness of the protective layer is not particularly limited but ispreferably in the range of 50 to 150 nm. When the thickness is less than50 nm, the mechanical strength is not sufficient, and when the thicknessis more than 150 nm, since the strength is excessively increased,pulverization/dispersion cannot be easily performed, so that peeling mayoccur at the interface with the aluminum layer in some cases.

In addition, as exemplified in JP-A-2005-68251, a coloring layer mayalso be provided between the “protective layer” and the “aluminumlayer”.

The coloring layer is provided to obtain an optional color compositepigment and is not particularly limited as long as it contains acoloring material which can impart optional color tone and hue inaddition to the metallic gloss, brightness, and background maskingproperties of the aluminum pigment used in this embodiment. As thecoloring material used for this coloring layer, either a dye or apigment may be used. In addition, as the dye or the pigment, a knownmaterial may be appropriately used.

In this case, the “pigment” used for the coloring layer indicates anatural pigment, a synthetic organic pigment, a synthetic inorganicpigment, or the like which is defined in general engineering fields.

A method for forming the coloring layer is not particularly limited, butthe coloring layer is preferably formed by coating. In addition, whenthe coloring material used for the coloring layer is a pigment, acoloring-material dispersion resin is preferably further contained. Whenthe coloring-material dispersion resin is used, a resin thin film ispreferably formed in such a way that after the pigment, thecoloring-material dispersion resin, and whenever necessary, otheradditives or the like are dispersed or dissolved in a solvent to form asolution, a uniform liquid film is formed by spin coating of thissolution, and drying is then performed. In addition, when the compositepigment base is manufactured, the coloring layer and the protectivelayer are preferably both formed by coating in view of workingefficiency.

The composite pigment base may also have a layer structure whichincludes a plurality of sequential lamination structures in each ofwhich the peeling resin layer and the aluminum layer are sequentiallylaminated. In this case, the total thickness of the laminationstructures including a plurality of aluminum layers, that is, thethickness of the aluminum layer-peeling resin layer-aluminum layer,which is obtained by removing the sheet-shaped substrate and the peelingresin layer provided immediately thereon, or the thickness of thepeeling resin layer-aluminum layer is preferably 5,000 nm or less. Whenthe thickness is 5,000 nm or less, even if the composite pigment base iswound in the form of a roll, cracking and peeling are not likely tooccur, and the storage stability is superior. In addition, when thecomposite pigment base is formed into a pigment, it is preferable sincethe metallic gloss is excellent. Although a structure in which thepeeling resin layers and the aluminum layers are sequentially laminatedon two surfaces of the sheet-shaped substrate may also be mentioned byway of example, the structure is not limited to those described above.

(2) Next, when the sheet-shaped substrate of the composite pigment baseis peeled away therefrom at the interface between the sheet-shapedsubstrate and the peeling resin layer in an organic solvent, and theremaining portion is processed by a pulverization or a particularizationtreatment, an aluminum pigment dispersion containing large and coarseparticles is obtained. Furthermore, when the aluminum pigment dispersionthus obtained is filtrated to remove large and coarse particles, analuminum pigment dispersion containing flat-shaped aluminum particlescan be obtained.

As the organic solvent, any solvent may be used as long as it does notimpair the dispersion stability of the aluminum pigment and/or thereactivity with tetraethoxysilane which will be described later, but apolar organic solvent is preferable. As the polar organic solvent, forexample, alcohols (methyl alcohol, ethyl alcohol, propyl alcohol, butylalcohol, isopropyl alcohol, fluorinated alcohols, and the like), ketones(acetone, methyl ethyl ketone, cyclohexanone, and the like), carboxylicacid esters (methyl acetate, ethyl acetate, propyl acetate, butylacetate, methyl propionate, ethyl propionate, and the like), and ethers(diethyl ether, dipropyl ether, tetrahydrofuran, dioxane, and the like)may be mentioned.

Among the polar organic solvents mentioned above by way of example, analkylene glycol monoether or an alkylene glycol diether which is aliquid at ordinary temperature and pressure is more preferable.

As the alkylene glycol monoether, for example, ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycolmonohexyl ether, ethylene glycol monophenyl ether, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycolmonobutyl ether, triethylene glycol monomethyl ether, triethylene glycolmonoethyl ether, triethylene glycol monobutyl ether, tetraethyleneglycol monomethyl ether, tetraethylene glycol monoethyl ether, propyleneglycol monomethyl ether, propylene glycol monoethyl ether, dipropyleneglycol monomethyl ether, or dipropylene glycol monoethyl ether may bementioned.

As the alkylene glycol diether, for example, ethylene glycol dimethylether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether,diethylene glycol dimethyl ether, diethylene glycol diethyl ether,diethylene glycol dibutyl ether, triethylene glycol dimethyl ether,triethylene glycol diethyl ether, triethylene glycol dibutyl ether,tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether,tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether,propylene glycol diethyl ether, dipropylene glycol dimethyl ether, ordipropylene glycol diethyl ether may be mentioned.

Among those mentioned above, since having superior dispersibilitystability of the aluminum pigment, triethylene glycol monobutyl ether ordiethylene glycol diethyl ether is more preferable. In addition, sincepreserving the gloss of the aluminum pigment and imparting the waterresistance thereto, diethylene glycol diethyl ether is particularlypreferable.

Although a peeling treatment performed on the sheet-shaped substrate isnot particularly limited, there may be preferably mentioned a method inwhich peeling is performed by immersing the composite pigment base in aliquid or a method in which when the composite pigment base is immersedin a liquid, an ultrasonic treatment is simultaneously performed toimplement a peeling treatment and a pulverization treatment of thepeeled composite pigment.

In the aluminum pigment including plate-shaped particles obtained asdescribed above, the peeling resin layer functions as protectivecolloid, and a stable dispersion can be obtained only by performing adispersing treatment in an organic solvent. In addition, when thealuminum pigment is used for an aqueous ink composition, a resin derivedfrom the peeling resin layer may also function to impart adhesion on arecording medium to the ink composition.

In order to impart superior water resistance and metallic gloss, thealuminum pigment in the aluminum pigment dispersion obtained by thesteps described above preferably includes plate-shaped particles.

When the long diameter, the short diameter, and the thickness of analuminum particle are represented by X, Y, and Z, respectively, the“plate-shaped particle” indicates a particle having an approximatelyflat surface (X-Y plain surface) and having an approximately constantthickness (Z). In more particular, the “plate-shaped particle” indicatesthat a 50% average particle diameter R50, which is the diameter of acorresponding circle obtained by calculation from the areas of theapproximately flat surfaces (X-Y plain surfaces) of the aluminumparticles, is in the range of 0.5 to 3 μm and that the thickness (Z) isin the range of 5 to 30 nm.

The “diameter of a corresponding circle” is the diameter of a circlewhich is assumed to have the same projection area as the projection areaof an aluminum particle having an approximately flat surface (X-Y plainsurface). For example, when an approximately flat surface (X-Y plainsurface) of an aluminum particle has a polygonal shape, a circle havingthe same projection area as that of the polygonal shape is assumed, andthe diameter of this circle is the “diameter of a corresponding circleof this aluminum particle”.

In order to ensure a superior metallic gloss and printing stability, the50% average particle diameter R50 of a corresponding circle obtained bycalculation from the areas of the approximately flat surfaces (X-Y plainsurfaces) of the plate-shaped particles is preferably in the range of0.5 to 3 μm and more preferably in the range of 0.75 to 2 μm. When R50is less than 0.5 μm, the metallic gloss may not be sufficient in somecases. On the other hand, when R50 is more than 3 μm, the printingstability may be degraded in some cases.

The maximum particle diameter of a corresponding circle obtained bycalculation from the areas of approximately flat surfaces (X-Y plainsurfaces) of the plate-shaped particles is preferably 10 μm or less.When the maximum particle diameter is set to 10 μm or less, nozzles ofan ink jet recording apparatus, foreign-substance removing filtersprovided in ink flow paths, and the like are prevented from beingclogged with the plate-shaped particles.

The long diameter X and the short diameter Y on the plain surface ofeach of the plate-shaped particles can be measured by a particle imageanalyzer. As the particle image analyzer, for example, a flow typeparticle image analyzer FPIA-2100, FPIA-3000, or FPIA-3000S(manufactured by Sysmex Corporation) may be mentioned.

The particle size distribution (CV value) of the plate-shaped particlescan be obtained by the following formula (6).CV value=(Standard deviation of particle size distribution/averageparticle diameter)×100  (6)

The CV value is preferably 60 or less, more preferably 50 or less, andparticularly preferably 40 or less. When plate-shaped particles having aCV value of 60 or less are selected, a superior printing stability canbe obtained.

In order to ensure the metallic gloss, the thickness (Z) is preferably 5to 30 nm and more preferably 10 to 25 nm. If the thickness (Z) is lessthan 5 nm, when a silica film is formed on the surface of the aluminumparticle, the metallic gloss tends to decrease. On the other hand, whenthe thickness (Z) is more than 30 nm, the metallic gloss also tends todecrease.

In view of the cost and in order to ensure the metallic gloss, thealuminum pigment is preferably composed of aluminum or an aluminumalloy. When an aluminum alloy is used, as another metal or non-metalelement to be added besides aluminum, for example, silver, gold,platinum, nickel, chromium, tin, zinc, indium, titanium, or copper maybe mentioned.

In this case, a step of washing an aluminum pigment contained in thealuminum pigment dispersion may be provided. For washing of the aluminumpigment, the organic solvent mentioned above may be used.

The peeling resin layer described above may be contained in the aluminumpigment dispersion, or the peeling resin layer may be adhered thereto insome cases. A component contained in the peeling resin layer may disturba reaction between the aluminum pigment and tetraethoxysilane which willbe described later. Hence, when the component of the peeling resin layeris removed by washing the aluminum pigment, the reactivity between thealuminum pigment and tetraethoxysilane which will be described later canbe improved.

A washing method of the aluminum pigment is not particularly limited,and for example, washing may be performed as described below.

First, at least part of the organic solvent is removed from the abovealuminum pigment dispersion. For the removal of the organic solvent, byoperation, such as filtration, centrifugal sedimentation, or centrifugalseparation, the organic solvent and the aluminum pigment are separatedfrom each other, so that the organic solvent contained in the aluminumpigment dispersion is removed.

Next, after an organic solvent for washing is added to the aluminumpigment so as to be dispersed therein, the organic solvent for washingis removed. In addition, the step of dispersing the aluminum pigment inthe solvent for washing and the step of removing the organic solvent forwashing may be performed at least twice.

Subsequently, when the organic solvent mentioned above is added so thatthe aluminum pigment is dispersed therein, an aluminum pigmentdispersion containing a washed aluminum pigment can be obtained.

(3) Next, tetraethoxysilane (hereinafter also referred to as “TEOS”) isadded in the aluminum pigment dispersion and is then stirred.Accordingly, a hydrolysis reaction occurs between TEOS and a hydroxylgroup present on the surface of the aluminum pigment, so that a silicafilm can be formed on the surface of the aluminum pigment. When thealuminum pigment is dispersed in water, a hydrogen gas is generated, andas a result, the aluminum pigment is whitened due to the generation ofalumina. Hence, the water resistance is imparted by covering the surfaceof the aluminum pigment with a silica film, and the metallic gloss ofthe aluminum pigment is prevented from being lost due the whiteningthereof.

The reaction temperature of the hydrolysis reaction is preferably 10° C.to 150° C. and more preferably 20° C. to 130° C. When the temperature isless than 10° C., since the hydrolysis reaction is slow, the formationof the silica film on the surface of the aluminum pigment is liable tobe insufficient. When the temperature is more than 150° C., particularattention must be paid from a safety point of view.

The reaction time of the hydrolysis reaction is preferably 0.5 to 200hours and more preferably 1 to 180 hours. When the reaction time is lessthan 0.5 hours, the hydrolysis reaction may not be sufficientlycompleted in some cases, and hence sufficient water resistance and waterdispersibility may not be obtained. When the reaction time is more than200 hours, the aluminum pigment may agglomerate in some cases.

The addition amount of TEOS may be determined by calculation so that thethickness of the silica film is 0.5 to 10 nm and preferably 5 nm. Thereason for this is that when the thickness of the silica film is morethan 10 nm, the metallic gloss may be decreased in some cases.

In particular, with respect to 1 part by mass of the aluminum pigment,the addition amount of TEOS is preferably 0.2 to 5 parts by mass, morepreferably 0.5 to 4 parts by mass, and even more preferably 1 to 3 partsby mass. When the addition amount of TEOS is more than 5 parts by mass,the aluminum pigment dispersion may be whitely clouded in some cases dueto unreacted TEOS. On the other hand, when the addition amount is lessthan 0.2 parts by mass, the hydroxyl group present on the surface of thealuminum pigment may not be completely covered in some cases.

In the first step, after TEOS is added, ammonia may also be added as abase catalyst. Ammonia can facilitate the hydrolysis reaction of TEOS.

With respect to 10 parts by mass of the aluminum pigment, the additionamount of ammonia is preferably 1 part by mass or less and morepreferably 0.1 parts by mass or less. When the addition amount ofammonia is more than the range described above, the viscosity of thealuminum pigment dispersion increases, and the aluminum pigment in thealuminum pigment dispersion agglomerates, so that the metallic glosscannot be maintained.

1.2. Second Step

In the second step of this embodiment, at least part of the organicsolvent is removed from the aluminum pigment dispersion.

For removal of the organic solvent, the aluminum pigment provided withthe silica film and the organic solvent are separated by operation, suchas filtration, centrifugal sedimentation, or centrifugal separation, sothat the organic solvent contained in the aluminum pigment dispersion isremoved. Among the operations mentioned above, since the centrifugalseparation is simple, the separation is preferably performed thereby toremove the organic solvent. By one of the methods described above, theorganic solvent contained in the aluminum pigment dispersion ispreferably removed in an amount of 70% or more and more preferably in anamount of 80% or more.

1.3. Third Step

In the third step of this embodiment, an aqueous surfactant solutionobtained by dissolving a surfactant in water is added to the aluminumpigment dispersion and is then sufficiently stirred. In this embodiment,the first step, the second step, and the third step are preferablyperformed in that order. The reason for this is that when the aqueoussurfactant solution is added in the third step after the second step isperformed, the agglomeration of the aluminum pigment can be effectivelyprevented, and the dispersibility of the water resistant aluminumpigment dispersion can be improved.

In this specification, the case in which the third step of adding anaqueous surfactant solution is performed after the second step isreferred to as “post-addition of surfactant”. On the other hand, withrespect to the post-addition of surfactant, the case in which the thirdstep of adding an aqueous surfactant solution is performed before thesecond step is referred to as “pre-addition of surfactant”. When thepre-addition of surfactant is performed, the effect of the surfactant isdisturbed by the influence of the organic solvent, and as a result, thealuminum pigment may agglomerate in some cases.

In this step, the organic solvent in the aluminum pigment dispersionobtained in the previous step can be changed to an aqueous solvent bysolvent replacement, so that a water resistant aluminum pigmentdispersion having superior water dispersibility can be obtained. Inaddition, since the solvent of the water resistant aluminum pigmentdispersion obtained in this step is an aqueous solvent base, the waterresistant aluminum pigment dispersion can be easily applied to anaqueous ink composition.

Although the stirring time after the addition of the aqueous surfactantsolution is not particularly limited, it is preferably 3 to 120 hours.When the stirring time is in the range described above, a waterresistant aluminum pigment dispersion having superior waterdispersibility can be obtained without degrading the metallic gloss.When the stirring time is more than 120 hours, the metallic gloss may bedegraded in some cases due to agglomeration of the aluminum pigment.

As the water, pure water or ultrapure water, such as ion exchange water,ultrafiltration water, reverse osmosis water, or distilled water, ispreferably used. In particular, water obtained by sterilizing the watermentioned above by ultraviolet radiation or addition of hydrogenperoxide is preferable since generation of fungi and bacteria can besuppressed for a long period of time.

As the surfactant, for example, an anionic surfactant, a cationicsurfactant, a non-ionic surfactant, an ampholytic surfactant, or a highmolecular weight surfactant may be used.

As the anionic surfactant, for example, there may be mentioned a higherfatty acid salt and an α-sulfo fatty acid methyl ester salt as a fattyacid-based surfactant; a liner alkylbenzene sulfonic acid salt as alinear alkylbenzene-based surfactant; an alkyl sulfuric ester salt, analkyl ether sulfuric ester salt, an alkyl phosphate ester salt, and adioctyl sulfosuccinate salt as a higher alcohol-based surfactant; anα-olefin sulfuric acid salt acid as an α-olefin-based surfactant; and analkane sulfonic acid salt as a normal paraffin-based surfactant.However, the anionic surfactant is not limited to those mentioned above.

As the cationic surfactant, for example, there may be mentioned an alkyltrimethyl ammonium salt, a dialkyl dimethyl ammonium salt, and an alkyldimethyl benzyl ammonium salt as a quaternary ammonium-based surfactant,and an N-methyl bis(hydroxyethyl)amine fatty acid ester hydrochloridesalt as an amine salt-based surfactant. However, the cationic surfactantis not limited to those mentioned above.

As the non-ionic surfactant, for example, there may be mentioned asucrose fatty acid ester, a sorbitan fatty acid ester, a polyoxyethylenesorbitan fatty acid ester, a polyoxyethylene fatty acid ester, and afatty acid alkanol amide as a fatty acid-based surfactant, and apolyoxyethylene alkyl ether, an alkyl glycoside, and a polyoxyethylenealkylphenyl ether as an ether-based surfactant. However, the non-ionicsurfactant is not limited to those mentioned above.

As the ampholytic surfactant, for example, there may be mentioned analkyl amino fatty acid salt as an amino acid-based surfactant, an alkylcarboxyl betaine as a betaine-based surfactant, and an alkylamine oxideas an amine oxide-based surfactant. However, the ampholytic surfactantis not limited to those mentioned above.

As the high molecular weight surfactant, for example, a polycarboxylicacid-based, a naphthalene-based, a melamine-based, and an aminosulfonicacid-based high molecular weight surfactant may be mentioned. As thepolycarboxylic acid-based surfactant, for example, there may bementioned a copolymer of acrylic acid, methacrylic acid, maleic acid, ormaleic anhydride with an olefin, styrene, or a polyoxyalkylene alkylether; a copolymer between acrylic acid and itaconic acid; a copolymerbetween methacrylic acid and itaconic acid; a copolymer between styreneand maleic acid or maleic anhydride; a copolymer between acrylic acidand methacrylic acid; a copolymer between acrylic acid and methylacrylate; a copolymer between acrylic acid and vinyl acetate; acopolymer between acrylic acid and maleic acid or maleic anhydride; or asalt thereof (such as an alkali metal, an alkali earth metal, anammonium, or an amine salt) may be mentioned. Those copolymers each maybe any one of an alternate copolymer, a random copolymer, a blockcopolymer, a graft copolymer, and the like.

As the surfactant, among those mentioned above, a high molecular weightsurfactant is preferable, at least one of polycarboxylic acids or saltsthereof is more preferable, and at least one selected from the groupconsisting of the following copolymers A, B, and C is particularlypreferable. The copolymers A, B, and C may be used alone or incombination.

The copolymers A, B, and C each have a bulky molecular structure. Hence,after being adsorbed on the surface of the aluminum pigment providedwith the silica film, the copolymers A, B, and C can effectivelysuppress agglomeration between particles of the aluminum pigmentprovided with the silica film by a steric hindrance function derivedfrom the molecular structure.

The copolymer A has a structural unit represented by the followinggeneral formula (1) or the following formula (2) and a structural unitrepresented by the general formula (3). The copolymer B has a structuralunit represented by the following general formula (1) or the followingformula (2) and a structural unit represented by the general formula(4). The copolymer C has a structural unit represented by the followinggeneral formula (1) or the following formula (2) and a structural unitrepresented by the general formula (5). The copolymers A, B, and C eachmay be any one of an alternate copolymer, a random copolymer, a blockcopolymer, a graft copolymer, and the like.

In the formula, A₁ and A₂ each independently indicate hydrogen, analkali metal, or ammonium.

In the formula, m indicates an integer of 1 to 5.

In the formula, n indicates an integer of 1 to 5.

In the formula, o indicates an integer of 1 to 5, and R indicates analkyl group.

In the general formula (3), m is an integer of 1 to 5 and is preferablyan integer of 1 to 3. In addition, n in the general formula (4) is aninteger of 1 to 5 and is preferably an integer of 1 to 3. In addition, oin the general formula (5) is an integer of 1 to 5 and is preferably aninteger of 1 to 3.

The weight average molecular weight of the copolymers A, B, and C areeach preferably 2,000 to 500,000, and more preferably 10,000 to 100,000.When the weight average molecular weights of the copolymers A, B, and Care each more than the above range, the viscosity of the water resistantaluminum pigment dispersion is increased, and the dispersibility thereofis degraded. On the other hand, when the weight average molecularweights of the copolymers A, B, and C are each less than the aboverange, the steric hindrance effect of the surfactant cannot be expected,and the dispersibility of the water resistant aluminum pigmentdispersion is degraded.

The weight average molecular weight is measured, for example, by a gelpermeation chromatography (GPC) using tetrahydrofuran as a solvent andcan be obtained as a polystyrene-converted molecular weight.

As the copolymer A, for example, Polystar-OM (trade name, manufacturedby NOF Corporation) may be mentioned which is a copolymer includingmaleic acid and an olefin as structural units. As the copolymer B, forexample, DSK-Discoat N-10 (trade name, manufactured by Dai-ichi KogyoSeiyaku Co., Ltd.) may be mentioned which is a copolymer includingmaleic acid and styrene as structural units. As the copolymer C, forexample, Malialim AKM-0531 (trade name, manufactured by NOF Corporation)may be mentioned which is a copolymer including maleic acid andpolyoxypropylene alkyl ether as structural units. In addition, as thecopolymer C, styrene may also be included as a structural unit.

With respect to 1 part by mass of the aluminum pigment, the additionamount of the surfactant is preferably 0.02 to 1.5 parts by mass, morepreferably 0.03 to 1.3 parts by mass, and even more preferably 0.03 to1.2 parts by mass. As the addition amount of the surfactant is more thanthe range described above, the dispersibility of the water resistantaluminum pigment dispersion may be degraded in some cases. On the otherhand, when the addition amount is less than the above range, thealuminum pigment agglomerates, and as a result, the metallic glosscannot be maintained.

With respect to the total mass of the water resistant aluminum pigmentdispersion, the addition amount of the aqueous surfactant solution ispreferably 70 mass percent or more and more preferably 80 mass percentor more.

2. Water Resistant Aluminum Pigment Dispersion

The water resistant aluminum pigment dispersion of this embodiment canbe manufactured by the manufacturing steps described above. The waterresistant aluminum pigment dispersion of this embodiment ischaracterized in that the water resistant aluminum pigment in which thealuminum pigment is covered with the silica film is dispersed in anaqueous solution containing at least one selected from the groupconsisting of the copolymers A, B, and C.

According to the water resistant aluminum pigment dispersion of thisembodiment, since the silica film is formed on the surface of thealuminum pigment, the water resistance is imparted thereto, and evenwhen being blended with an aqueous paint or an aqueous ink composition,the metallic gloss is not degraded. In addition, since the aluminumpigment covered with the silica film is dispersed in an aqueous solutioncontaining at least one selected from the group consisting of thecopolymers A, B, and C, a water resistant aluminum pigment dispersionhaving superior water dispersibility can be obtained without degradingthe water resistance and the metallic gloss.

The water resistant aluminum pigment may be an aluminum pigmentprocessed by a surface treatment using tetraethoxysilane. As describedabove, when the surface of the aluminum pigment is processed bytetraethoxysilane, a water resistant aluminum pigment having superiorwater resistance can be obtained.

The aluminum pigment preferably includes plate-shaped aluminum particleshaving an average thickness of 5 to 30 nm and a 50% average particlediameter (R50) of 0.5 to 3 μm.

As described above, when the average thickness of the particles of thealuminum pigment is 5 to 30 nm, a water resistant aluminum pigmenthaving a superior metallic gloss can be formed. On the other hand, whenthe average thickness is less than 5 nm, the metallic gloss tends todecrease, and when the average thickness is more than 30 nm, themetallic gloss also tends to decrease.

As described above, when R50 of the aluminum pigment is 0.5 to 3 μm, asuperior metallic gloss and printing stability can be ensured. When R50is less than 0.5 μm, the metallic gloss may become insufficient. On theother hand, when R50 is more than 3 μm, the printing stability may bedegraded in some cases.

The thickness of the silica film is preferably 0.5 to 10 nm and morepreferably 1 to 9 nm. When the thickness of the silica film is less than0.5 nm, sufficient water resistance and water dispersibility cannot beimparted to the aluminum pigment. On the other hand, when the thicknessof the silica film is more than 10 nm, although the water resistance andthe water dispersibility can be imparted to the aluminum pigment, themetallic gloss tends to decrease.

The surface condition of the water resistant aluminum pigment of thisembodiment can be identified by an element analysis using an X-rayphotoelectron spectroscopic method (hereinafter referred to as “XPS”).The principle of XPS will be roughly described.

XPS is a spectroscopic method in which energy of photoelectrons emittedfrom a sample by radiation of X-rays is measured. In the air,photoelectrons immediately collide with molecules and are scattered;hence, the inside of an apparatus must be placed in an evacuated state.In addition, photoelectrons emitted from a very deep position of a solidsample are scattered inside the sample and cannot escape therefrom.Accordingly, photoelectrons emitted only from a sample surface aremeasured by XPS, and hence XPS is an effective surface analyticalmethod. In XPS, the range from the sample surface to a depth of severalnanometers can be analyzed.

The kinetic energy E of a photoelectron which is observed is the valueobtained by subtracting energy φ required to transfer an electronlocated in the crystal to the outside of the sample surface fromhν-E_(K), that is, the value represented by the following formula.E=hν−E _(K)−φ(7)In this formula, h indicates Planck's constant, ν indicates the numberof frequency, and E_(K) indicates the electron bond energy. From theabove formula (7), it is understood that the value E varies depending onthe energy of X-rays from an excitation source. As excited X-rays, ingeneral, characteristic X-rays from an X-ray tube using an aluminum or amagnesium target are used. Although a measurement method of the electronenergy is not particularly limited, as a representative method, theremay be mentioned an electrostatic field method in which after electronsare introduced into an electrostatic field, only an electron movingalong a predetermined trajectory is detected.

By XPS, the electron bond energy E_(K) can be measured. Since the bondenergy described above is fundamentally an intrinsic value of eachelement, the type of element can be identified. In addition, from theintensities of photoelectron spectra, the quantities of individualelements can also be determined.

Although incident X-rays enter the inside of a sample from the surfacethereof, the mean free paths of excited photoelectrons are small such as0.1 to several nanometers, and hence photoelectrons are emitted onlyfrom the vicinity of the sample surface. Hence, the analysis in thevicinity of the sample surface can be performed. However, in the case inwhich a plurality of layers is present in the vicinity of the samplesurface, even when it is attempted to measure a small composition amountof each layer, accurate measurement may not be performed in some cases.The reason for this is that in the XPS measurement, a relativecomposition amount which is the average amount from the surface to adepth of several tens of angstroms is measured. When the compositions ofseveral layers from the surface are measured, an angle dependence of theescape depth of photoelectrons may be used. That is, althoughphotoelectrons are isotropically emitted from the sample surface, theescape depth of photoelectrons emitted from the solid surface variesdepending on the photoelectron takeoff angle. When this phenomenon isused, the escape depth is decreased as the photoelectron takeoff angleis changed from the direction perpendicular to the sample surface to theinclined direction, and hence information in the vicinity closer to thesample surface can be obtained.

In this embodiment, the “photoelectron takeoff angle” indicates an angleformed between the sample surface and a detector. FIGS. 1A and 1B areviews each schematically showing the photoelectron takeoff angle in theXPS measurement.

FIG. 1A shows the case in which the photoelectron takeoff angle is 90°.As shown in FIG. 1A, “the photoelectron takeoff angle is 90° ” indicatesthe case in which an angle θ formed between a detector 20 and a surface10 a of a sample 10 is 90°. As shown in FIG. 1A, the escape depth ofphotoelectrons is maximized, and information from the sample surface 10a to a depth D can be detected.

FIG. 1B shows the case in which the photoelectron takeoff angle is 30°.As shown in FIG. 1B, in order to set the photoelectron takeoff angle to30°, after the position of the detector 20 is fixed, adjustment wasperformed by inclining the sample 10 with respect to the detector 20. Inthe case of a photoelectron takeoff angle of 30°, an escape depth d ofphotoelectrons satisfies the formula represented by d=D·sin 30°=0.5D.Accordingly, since the escape depth is decreased when the photoelectrontakeoff angle is set to 30°, information in the vicinity closer to thesurface can be detected.

In the water resistant aluminum pigment dispersion of this embodiment,since the thickness of the silica film covering the aluminum pigment ispreferably 0.5 to 10 nm as described above, although depending on thetype of XPS apparatus, the photoelectron takeoff angle is preferably setto 10° to less than 45°. When the photoelectron takeoff angle is set inthe range described above, the condition in the vicinity closer to thesurface of the water resistant aluminum pigment can be identified.

The covering rate of the silica film on the surface of the waterresistant aluminum pigment can be calculated from composition ratios ofC, O, Al, and Si elements measured by XPS.

Hereinafter, a method for obtaining the covering rate of the silica filmon the surface of the water resistant aluminum pigment from thecomposition ratios of C, O, Al, and Si elements measured by XPS will bedescribed.

First, the composition ratios of C, O, Al, and Si elements obtained bythe XPS measurement can be interpreted as follows.

(1) Al

Aluminum can be categorized into an Al element (Al) which is not bondedto oxygen and Al (Al₀) which is bonded to oxygen. After the peaks ofAl-2p spectrum are separated, from the area ratio between the separatedpeaks, the ratio of the Al element (Al) which is not bonded to oxygenand the Al (Al₀) which is bonded to oxygen can be obtained.

(2) Si

Si can be categorized as Si (Si₁) derived from TEOS.

(3) O

Oxygen can be categorized into O (O₀) bonded to Al and O (O₁) bonded toSi.

(4) C

The detected C is parts of the organic solvent, the surfactant, and thelike and cannot be considered as responsible for the formation of thecoating film.

From the categorized elements described above, the covering rate of thesilica film on the surface of the water resistant aluminum pigment canbe obtained by the following formula (8).Covering Rate (%)=[(Si₁+O₁)/{(Si₁+O₁)+(Al)+(Al₀+O₀)}]×100  (8)

The covering rate of the silica film on the water resistant aluminumpigment of this embodiment calculated by the above formula (8) ispreferably 30% to 90% and more preferably 50% to 90%. When the coveringrage is within the range described above, the water resistance can beimparted to the aluminum pigment, and even when being dispersed inwater, the aluminum pigment is not whitened. When the covering rate isless than 30%, since a sufficient water resistance cannot be obtained,the aluminum pigment may be whitened, and/or since sufficient waterdispersibility is not obtained, the aluminum pigment may be blackeneddue to the agglomeration thereof. On the other hand, in order to obtaina covering rate of more than 90%, technical difficulties may arise.

3. Aqueous Ink Composition

The aqueous ink composition of this embodiment is characterized in thatthe water resistant aluminum pigment dispersion described above iscontained. In this specification, the “aqueous ink composition”indicates an ink composition containing 70 mass percent or more of wateras a solvent. As the water, pure water or ultrapure water, such as ionexchange water, ultrafiltration water, reverse osmosis water, ordistilled water, is preferably used. In particular, water obtained bysterilizing the water mentioned above by ultraviolet radiation oraddition of hydrogen peroxide is preferable since generation of fungiand bacteria can be suppressed for a long period of time.

With respect to the total mass of the aqueous ink composition, theconcentration of the aluminum pigment in the aqueous ink composition ofthis embodiment is preferably 0.1 to 3.0 mass percent, more preferably0.25 to 2.5 mass percent, and particularly preferably 0.5 to 2.0 masspercent.

The aqueous ink composition of this embodiment may contain a resin or aderivative thereof, a surfactant, an alkanediol, a polyalcohol, a pHadjuster, and the like.

The resin or its derivative functions to tightly fix the aluminumpigment to a recording medium. As a component of the resin or itsderivative, for example, there may be mentioned a homopolymer or acopolymer of acrylic acid, an acrylic ester, methacrylic acid, amethacrylic ester, acrylonitrile, cyanoacrylate, acrylamide, an olefin,styrene, vinyl acetate, vinyl chloride, vinyl alcohol, vinyl ether,vinyl pyrrolidone, vinyl pyridine, vinyl carbazole, vinyl imidazole,vinylidene chloride, or the like, a urethane resin, a fluorinated resin,or a natural resin. In addition, as the copolymer, any one of a randomcopolymer, a block copolymer, an alternate copolymer, and a graftcopolymer may be used.

As the surfactant, an acetylene glycol-based surfactant or apolysiloxane-based surfactant is preferably contained. The acetyleneglycol-based surfactant and the polysiloxane-based surfactant canenhance an impregnation property of ink by improving the wettability toa recording surface of a recording medium or the like. As the acetyleneglycol-based surfactant, for example, there may be mentioned2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol,3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol. In addition,as the acetylene glycol-based surfactant, a commercially availableproduct may also be used, and for example, there may be mentioned OlfinE1010, STG, and Y (all manufactured by Nisshin Chemical Co., Ltd.) andSurfinol 104, 82, 465, 485, and TG (all manufactured by Air Products andChemicals Inc.) As the polysiloxane-based surfactant, a commerciallyavailable product may be used, and for example, there may be mentionedBYK-347 and BYK-348 (manufactured by BYK Japan K.K.). Furthermore, theaqueous ink composition may also contain another surfactant, such as ananionic surfactant, a nonionic surfactant, or an ampholytic surfactant.

An alkanediol can enhance the impregnation property of ink by improvingthe wettability to a recording surface of a recording medium or thelike. As the alkanediol, a 1,2-alkanediol having 4 to 8 carbon atoms,such as 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol,1,2-heptanediol, or 1,2-octanediol, is preferable. Among those mentionedabove, 1,2-hexanediol, 1,2-heptanediol, or 1,2-octanediol is morepreferable since its impregnation property to a recording medium isparticularly superior.

For example, when an aqueous ink composition is applied to an ink jetrecording apparatus, a polyalcohol can suppress the aqueous inkcomposition from being dried and/or can prevent the aqueous inkcomposition from clogging an ink jet recording head portion. As thepolyalcohol, for example, ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, polypropylene glycol, propyleneglycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol,glycerin, trimethylolethane, and trimethylolpropane may be mentioned.

As the pH adjuster, for example, there may be mentioned potassiumdihydrogen phosphate, disodium hydrogenphosphate, sodium hydroxide,lithium hydroxide, potassium hydroxide, ammonia, diethanolamine,triethanolamine, triisopropanolamine, potassium carbonate, sodiumcarbonate, or sodium hydrogen carbonate.

In addition, the aqueous ink composition of this embodiment may alsocontain at least one additive, such as a fixing agent including awater-soluble rosin, a fungicide/antiseptic including sodium benzoate,an antioxidant/UV absorber including an allophanate or a derivativethereof, a chelating agent, or an oxygen absorber. Those additives maybe used alone, and of course, at least two of them may be used incombination.

Applications of the aqueous ink composition of this embodiment are notparticularly limited, and for example, the aqueous ink composition maybe applied, for example, to a writing tool, a stamp, a recorder, a penplotter, and an ink jet recording apparatus.

The viscosity of the aqueous ink composition of this embodiment at 20°C. is preferably in the range of 2 to 10 mPa·s and more preferably inthe range of 3 to 5 mPa·s. When the viscosity of the aqueous inkcomposition at 20° C. is in the range described above, an appropriateamount of the aqueous ink composition can be ejected from a nozzle, andtrajectory deviation and scattering of the aqueous ink composition canbe further reduced, so that the aqueous ink composition of thisembodiment can be preferably used for an ink jet recording apparatus.

4. Examples 4.1 Example 1

A resin-layer coating liquid containing 3.0 mass percent of celluloseacetate butyrate (butylation rate: 35% to 39%, manufactured by KantoChemical Co., Inc.) and 97 mass percent of diethylene glycol diethylether (manufactured by Nippon Nyukazai Co., Ltd.) was uniformly appliedon a PET film having a thickness of 100 μm by a bar-coating method andwas then dried at 60° C. for 10 minutes, so that a resin layer thin filmwas formed on the PET film.

Next, an aluminum deposition layer having an average film thickness of20 nm was formed on the above resin layer using a vacuum depositionapparatus (“VE-1010 type vacuum deposition apparatus” manufactured byVacuum Device Inc.).

Next, the laminate formed by the method described above wassimultaneously processed by peeling, particularization, and dispersiontreatments using an ultrasonic dispersion apparatus VS-150 (manufacturedby AS ONE Corporation) in diethylene glycol diethyl ether, and as aresult, an aluminum pigment dispersion was obtained when a cumulativeultrasonic dispersion time was 12 hours.

The aluminum pigment dispersion thus obtained was processed by afiltration treatment using a SUS mesh filter with 5-μm openings, so thatcoarse and large particles were removed. Next, the filtrate was receivedin a round-bottom flask, and diethylene glycol diethyl ether wasdistilled out using a rotary evaporator. After the aluminum pigmentdispersion was concentrated by the above step, the concentration of thealuminum pigment dispersion thus concentrated was adjusted, so that analuminum pigment dispersion at a concentration of 5.0 mass percent wasobtained.

Subsequently, after 5.0 g of the obtained aluminum pigment dispersionwas charged in a beaker, and 0.57 g of TEOS which was a silica rawmaterial and 0.1 g of ammonia water at a concentration of 1 mol/L whichwas a base catalyst were then added in the beaker, a hydrolysis reactionwas performed by stirring at room temperature for 7 days. As a result,an aluminum pigment dispersion was obtained in which the surface of thealuminum pigment was covered with a silica film.

Next, the dispersion thus obtained was processed by centrifugalseparation (10,000 rpm, 60 minutes), and as a result, the solventcontained in the aluminum pigment dispersion in which the silica filmwas formed was removed. Subsequently, while stirring was performed, anaqueous solution containing 0.2 mass percent of Polystar-OM (hereinafterreferred to as “0.2% Polystar-OM aqueous solution”) was added as asurfactant in an amount which was calculated so that the concentrationof the aluminum pigment was 1.7 mass percent. As described above, awater resistant aluminum pigment dispersion A was obtained.

4.2 Example 2

Except that instead of the 0.2% Polystar-OM aqueous solution, an aqueoussolution containing 1 mass percent of Polystar-OM (hereinafter referredto as “1% Polystar-OM aqueous solution”) was used, a water resistantaluminum pigment dispersion B was obtained in a manner similar to thatin the “4.1 Example 1”.

Next, the water resistant aluminum pigment dispersion B thus obtainedwas equally divided into two portions, that is, water resistant aluminumpigment dispersions B-1 and B-2.

4.3 Example 3

Except that instead of the 0.2% Polystar-OM aqueous solution, an aqueoussolution containing 2 mass percent of Polystar-OM was used, a waterresistant aluminum pigment dispersion C was obtained in a manner similarto that in the “4.1 Example 1”.

4.4 Example 4

In Example 4, after 5 g of the aluminum pigment dispersion at aconcentration of 5.0 mass percent which was prepared in the “4.1 Example1” was charged in a beaker, 0.57 g of TEOS and 0.1 g of ammonium waterat a concentration of 0.1 mol/L were added and were stirred at roomtemperature for 7 days, so that a hydrolysis reaction was carried out.As a result, an aluminum pigment dispersion in which a silica film wasformed on the surface of the aluminum pigment was obtained.

Next, the aluminum pigment dispersion was processed by centrifugalseparation (10,000 rpm, 60 minutes), so that the solvent contained inthe aluminum pigment dispersion in which the silica film was formed wasremoved. Subsequently, while stirring was performed, the 0.26 Polystaraqueous solution was added in an amount which was calculated so as toobtain an aluminum pigment concentration of 5.0 mass percent.Accordingly, a water resistant aluminum pigment dispersion D wasobtained.

4.5 Example 5

Except that instead of Polystar-OM, Malialim AKM-0531 was used, a waterresistant aluminum pigment dispersion E was obtained in a manner similarto that in the “4.1 Example 1”.

4.6 Example 6

Except that instead of Polystar-OM, Malialim AKM-0531 was used, a waterresistant aluminum pigment dispersion F was obtained in a manner similarto that in the “4.2 Example 2”.

4.7 Example 7

Except that the base catalyst was not added, a water resistant aluminumpigment dispersion G was obtained in a manner similar to that in the“4.1 Example 1”.

4.8 Example 8

Except that instead of the 0.2% Polystar-OM aqueous solution, an aqueoussolution containing 0.1 mass percent of DSK-Discoat N-10 was used, awater resistant aluminum pigment dispersion H was obtained in a mannersimilar to that in the “4.1 Example 1”.

4.9 Example 9

Except that instead of Polystar-OM, DSK-Discoat N-10 was used, a waterresistant aluminum pigment dispersion I was obtained in a manner similarto that in the “4.2 Example 2”.

4.10 Example 10

In Example 10, after the aluminum pigment dispersion at a concentrationof 5.0 mass percent which was prepared in the “4.1 Example 1” wasprocessed by centrifugal separation (12,000 rpm, 30 minutes), so thatthe solvent contained in the aluminum pigment dispersion was removed.

Subsequently, after tetrahydrofuran, which was an organic solvent usedfor washing, was added to the aluminum pigment thus separated, andstirring was performed for 24 hours, centrifugal separation wasperformed (12,000 rpm, 30 minutes), so that tetrahydrofuran was removed.The operation described above was performed twice.

Next, diethylene glycol diethyl ether was added to the aluminum pigment,and as a result, an aluminum pigment dispersion at a concentration of5.0 mass percent was obtained.

Subsequently, after 5.0 g of the obtained aluminum pigment dispersionwas charged in a beaker, 0.57 g of TEOS and 0.1 g of ammonia water at aconcentration of 1 mol/L were added, and stirring was performed at roomtemperature for 6 days. Next, the temperature was increased, andstirring was performed at 105° C. for 5 hours, so that a hydrolysisreaction was carried out. As a result, an aluminum pigment dispersionwas obtained in which the surface of the aluminum pigment was coveredwith a silica film.

Next, the dispersion thus obtained was processed by centrifugalseparation (10,000 rpm, 60 minutes), and as a result, the solventcontained in the aluminum pigment dispersion in which the silica filmwas formed was removed. Subsequently, while stirring was performed, the195 Polystar-OM aqueous solution was added in an amount which wascalculated so that the concentration of the aluminum pigment was 1.7mass percent. As described above, a water resistant aluminum pigmentdispersion J was obtained.

4.11 Example 11

Except that the conditions of the hydrolysis reaction in the “4.10Example 10” were changed in such a way that after stirring was performedat room temperature for 6 days, and the temperature was then increased,stirring was performed at 105° C. for 4 hours, and that after thetemperature was further increased, stirring was performed at 115° C. for5 hours, a water resistant aluminum pigment dispersion K was obtained ina manner similar to that in the “4.10 Example 10”.

4.12 Comparative Example 1

Except that TEOS was not added, a water resistant aluminum pigmentdispersion L was obtained in a manner similar to that in the “4.4Example 4”.

4.13 Comparative Example 2

In Comparative Example 2, after 5 g of the aluminum pigment dispersionat a concentration of 5.0 mass percent which was prepared in the “4.1Example 1” was charged in a beaker, 0.57 g of TEOS and 0.1 g of ammoniumwater at a concentration of 1 mol/L were added thereto, and stirring wasperformed at room temperature for 1 day, so that a hydrolysis reactionwas carried out.

Next, centrifugal separation (10,000 rpm, 60 minutes) was performed, sothat the solvent was removed. Subsequently, while stirring wasperformed, distilled water was added so that the concentration of thealuminum pigment was 5.0 mass percent. Accordingly, a water resistantaluminum pigment dispersion M was obtained.

4.14 Comparative Example 3

Except that instead of Polystar-OM, Ceramo D-134 (ammonium polyacrylate,manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used, a waterresistant aluminum pigment dispersion N was obtained in a manner similarto that in the “4.2 Example 2”.

4.15 Comparative Example 4

Except that instead of Polystar-OM, Shallol AH-103P (ammoniumpolyacrylate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) wasused, a water resistant aluminum pigment dispersion O was obtained in amanner similar to that in the “4.2 Example 2”.

4.16 Comparative Example 5

Except that instead of Polystar-OM, Discoat N-509 (polyalkylenepolyamine alkylene oxide adduct, manufactured by Dai-ichi Kogyo SeiyakuCo., Ltd.) was used, a water resistant aluminum pigment dispersion P wasobtained in a manner similar to that in the “4.2 Example 2”.

4.17 Comparative Example 6

Except that instead of Polystar-OM, Pitzcol K-30L (polyvinylpyrrolidone,manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used, a waterresistant aluminum pigment dispersion Q was obtained in a manner similarto that in the “4.2 Example 2”.

4.18 Comparative Example 7

Except that instead of Polystar-OM, Plysurf M-208B (Polyoxyethylenelauryl ether phosphate ester monoethanolamine salt, manufactured byDai-ichi Kogyo Seiyaku Co., Ltd.) was used, a water resistant aluminumpigment dispersion R was obtained in a manner similar to that in the“4.2 Example 2”.

4.19 Comparative Example 8

Except that ammonium water at a concentration of 0.1 mol/L (basecatalyst) was not added, a water resistant aluminum pigment dispersion Swas obtained in a manner similar to that in the “4.13 ComparativeExample 2”.

4.20 Comparative Example 9

Except that instead of ammonium water at a concentration of 0.1 mol/L,0.04 g of diethylamine was added, a water resistant aluminum pigmentdispersion T was obtained in a manner similar to that in the “4.13Comparative Example 2”.

4.21 Comparative Example 10

Except that instead of TEOS, 0.57 g of tetramethoxysilane (hereinafteralso referred to as “TMOS”) was added, a water resistant aluminumpigment dispersion U was obtained in a manner similar to that in the“4.13 Comparative Example 2”.

4.22 Comparative Example 11

Except that instead of TEOS, 0.57 g of methyl silicate 51 (methylsilicate condensed product, manufactured by Fuso Chemical Co., Ltd.) wasadded, a water resistant aluminum pigment dispersion V was obtained in amanner similar to that in the “4.13 Comparative Example 2”.

4.23 Reference Example 1

In Reference Example 1, after 5.0 g of the aluminum pigment dispersionat a concentration of 5.0 mass percent which was prepared in the “4.1Example 1” was charged in a beaker, 0.57 g of TEOS and 0.1 g of ammoniawater at a concentration of 1 mol/L were then added in the beaker, and ahydrolysis reaction was performed by stirring at room temperature for 1day. Next, after the 1% Polystar-OM aqueous solution was added, stirringwas performed at room temperature for 5 days (pre-addition ofsurfactant). Subsequently, after the solvent was removed by centrifugalseparation (10,000 rpm, 60 minutes), while stirring was performed,distilled water was added so that the aluminum pigment had aconcentration of 5.0 mass percent. As a result, a water resistantaluminum pigment dispersion W was obtained.

4.24 Reference Example 2

Except that the surfactant was changed from Polystar-OM to MalialimAKM-0531, a water resistant aluminum pigment dispersion X was obtainedin a manner similar to that in the “4.23 Reference Example 1”.

4.25 Evaluation tests 4.25.1 Water Resistance Evaluation Test

After 2 mL of water was charged in a sample bottle, and 2 mL of one ofthe water resistant aluminum pigment dispersions (hereinafter simplyreferred to as “dispersions”) A to X was further dripped, the mixturethus obtained was held at a constant temperature of 25° C. The changewith time was observed by visual inspection, so that the waterresistance of the dispersion was evaluated. The evaluation criteria areas follows. The results of the water resistance evaluation test areshown in Tables 1 to 3.

-   “AAA” Significantly superior water resistance (no whitening after 70    days)-   “AA” Superior water resistance (no whitening after 30 days)-   “A” Slightly superior water resistance (no whitening after 10 days)-   “B” Inferior water resistance (occurrence of whitening after 10    days)-   “C” Markedly inferior water resistance (occurrence of whitening    after 7 days)

4.25.2 Dispersibility Evaluation Test

After 2 mL of water was charged in a sample bottle, and 2 mL of one ofthe obtained dispersions A to X was further dripped, the mixture thusobtained was held at a constant temperature of 25° C. The change withtime was observed by visual inspection, so that the dispersibility ofthe dispersion was evaluated. The dispersibility of the dispersion wasevaluated by an increase in viscosity thereof and blackening of thedispersion due to agglomeration among aluminum pigment particles. Theevaluation criteria are as follows. The results of the dispersibilityevaluation test are shown in Tables 1 to 3.

-   “AAA” Significantly superior dispersibility-   “AA” Superior dispersibility-   “A” Slightly superior dispersibility-   “B” Inferior dispersibility-   “C” Markedly inferior dispersibility

4.25.3 Gloss Evaluation Test

After one of the dispersions A to X was dripped/applied to printingpaper (PM photo paper (gloss) model No. KA450PSK, manufactured by SeikoEpson Corporation), drying was performed at room temperature for 1 day.The sample thus obtained was observed by visual inspection and ascanning electron microscope (S-4700 manufactured by HitachiHigh-Technologies Corporation, hereinafter referred to as “SEM”), sothat the gloss of the aluminum pigment was evaluated. The evaluationcriteria of the gloss of the aluminum pigment are as follows. Theresults of the gloss evaluation test are shown in Tables 1 to 3.

-   “AA” Superior gloss (having superior metallic gloss and mirror    surface gloss)-   “A” Slightly superior gloss (having superior metallic gloss but    slightly matte touch)-   “B” Inferior gloss (having matte touch)

TABLE 1 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 TYPE OF WATERRESISTANT A B-1 B-2 C D E ALUMINUM PIGMENT DISPERSION ALUMINUM PIGMENTCONCENTRATION 1.7 1.7 1.7 5.0 1.7 (MASS PERCENT) SURFACTANT TYPEPOLYSTAR- POLYSTAR- POLYSTAR- POLYSTAR- MALIALIM OM OM OM OM AKM-0531ADDITION AMOUNT 0.19 0.94 1.88 0.16 0.19 (MASS PERCENT) ADDITION TIMINGPOST- POST- POST- POST- POST- ADDITION ADDITION ADDITION ADDITIONADDITION SILICA RAW TYPE TEOS TEOS TEOS TEOS TEOS MATERIAL ADDITIONAMOUNT 3.9 3.9 3.9 11.4 3.9 (MASS PERCENT) BASE TYPE 0.1 mol/L 0.1 mol/L0.1 mol/L 0.1 mol/L 0.1 mol/L CATALYST NH₃aq NH₃aq NH₃aq NH₃aq NH₃aqADDITION AMOUNT 0.68 0.68 0.68 2.0 0.68 (MASS PERCENT) EVALUATION WATERRESISTANCE AAA AAA AAA AA AAA AAA RESULT (WHITENING TEST) DISPERSIBILITYAA AAA AAA A AA A GLOSS AA AA AA A A AA EXAMPLE 6 EXAMPLE 7 EXAMPLE 8EXAMPLE 9 EXAMPLE 10 EXAMPLE 11 TYPE OF WATER RESISTANT F G H I J KALUMINUM PIGMENT DISPERSION ALUMINUM PIGMENT CONCENTRATION 1.7 1.7 1.71.7 1.7 1.7 (MASS PERCENT) SURFACTANT TYPE MALIALIM POLYSTAR- DSK- DSK-POLYSTAR- POLYSTAR- AKM-0531 OM DISCOAT DISCOAT OM OM N-10 N-10 ADDITIONAMOUNT 0.94 0.19 0.095 0.94 0.94 0.94 (MASS PERCENT) ADDITION TIMINGPOST- POST- POST- POST- POST- POST- ADDITION ADDITION ADDITION ADDITIONADDITION ADDITION SILICA RAW TYPE TEOS TEOS TEOS TEOS TEOS TEOS MATERIALADDITION AMOUNT 3.9 3.9 3.9 3.9 3.9 3.9 (MASS PERCENT) BASE TYPE 0.1mol/L — 0.1 mol/L 0.1 mol/L 0.1 mol/L 0.1 mol/L CATALYST NH₃aq NH₃aqNH₃aq NH₃aq NH₃aq ADDITION AMOUNT 0.68 — 0.68 0.68 0.68 0.68 (MASSPERCENT) EVALUATION WATER RESISTANCE AAA AA AAA AAA AAA AAA RESULT(WHITENING TEST) DISPERSIBILITY AA AA AAA AA AAA AAA GLOSS AA AA AA AAAA AA

TABLE 2 COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- ATIVE ATIVEATIVE ATIVE ATIVE ATIVE EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE5 EXAMPLE 6 TYPE OF WATER RESISTANT L M N O P Q ALUMINUM PIGMENTDISPERSION ALUMINUM PIGMENT CONCENTRATION 5.0 5.0 1.7 1.7 1.7 1.7 (MASSPERCENT) SURFACTANT TYPE POLYSTAR- — CERAMO SHALLOL DISCOAT PITZCOL OMD-134 AH-103P N-509 K-30L ADDITION AMOUNT 0.18 — 0.94 0.94 0.94 0.94(MASS PERCENT) ADDITION TIMING POST- — POST- POST- POST- POST- ADDITIONADDITION ADDITION ADDITION ADDITION SILICA RAW TYPE — TEOS TEOS TEOSTEOS TEOS MATERIAL ADDITION AMOUNT — 11.4 3.9 3.9 3.9 3.9 (MASS PERCENT)BASE TYPE 0.1 mol/L 0.1 mol/L 0.1 mol/L 0.1 mol/L 0.1 mol/L 0.1 mol/LCATALYST NH₃aq NH₃aq NH₃aq NH₃aq NH₃aq NH₃aq ADDITION AMOUNT 2.0 2.00.68 0.68 0.68 0.68 (MASS PERCENT) EVALUATION WATER RESISTANCE C A A AAAA AA RESULT (WHITENING TEST) DISPERSIBILITY AA B C C B C GLOSS AA B B BB B COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- ATIVE ATIVE ATIVE ATIVEATIVE EXAMPLE 7 EXAMPLE 8 EXAMPLE 9 EXAMPLE 10 EXAMPLE 11 TYPE OF WATERRESISTANT R S T U V ALUMINUM PIGMENT DISPERSION ALUMINUM PIGMENTCONCENTRATION 1.7 5.0 5.0 5.0 5.0 (MASS PERCENT) SURFACTANT TYPE PLYSURFM- — — — — 208B ADDITION AMOUNT 0.94 — — — — (MASS PERCENT) ADDITIONTIMING POST- — — — — ADDITION SILICA RAW TYPE TEOS TEOS TEOS TEOS METHYLMATERIAL SILICATE 51 ADDITION AMOUNT 3.9 11.4 11.4 11.4 11.4 (MASSPERCENT) BASE TYPE 0.1 mol/L — DIETHYLAMINE 0.1 mol/L 0.1 mol/L CATALYSTNH₃aq NH₃aq NH₃aq ADDITION AMOUNT 0.68 — 0.8 2.0 2.0 (MASS PERCENT)EVALUATION WATER RESISTANCE AAA A — B A RESULT (WHITENING TEST)DISPERSIBILITY C B C A C GLOSS C B — A B

TABLE 3 REFERENCE REFERENCE EXAMPLE 1 EXAMPLE 2 TYPE OF WATER RESISTANTW X ALUMINUM PIGMENT DISPERSION ALUMINUM PIGMENT 5.0 5.0 CONCENTRATION(MASS PERCENT) SURFACTANT TYPE POLYSTAR- MALIALIM OM AKM-0531 ADDITION0.82 0.82 AMOUNT (MASS PERCENT) ADDITION PRE- PRE- TIMING ADDITIONADDITION SILICA RAW TYPE TEOS TEOS MATERIAL ADDITION 11.4 11.4 AMOUNT(MASS PERCENT) BASE TYPE 0.1 mol/L 0.1 mol/L CATALYST NH₃aq NH₃aqADDITION 2.0 2.0 AMOUNT (MASS PERCENT) EVALUATION WATER A AA RESULTRESISTANCE (WHITENING TEST) DISPERSIBILITY B B GLOSS B B

4.25.4 Measurement of Covering Rate of Silica Film

(1) Measurement Conditions 1

One of the dispersions A to G, J to M, and S to X which were obtainedimmediately after the process described above was dripped to apolytetrafluoroethylene-made membrane filter and was then dried, so thata sample for measuring a covering rate was obtained. Next, the samplefor measuring a covering rate was fixed to a sample stage of an X-rayphotoelectron spectroscopic apparatus described below, and the presenceratios of C, O, Si, and Al of the surface of the water resistantaluminum pigment were measured under the following measurementconditions 1.

Measurement Conditions 1

-   -   X-ray photoelectron spectroscopic apparatus: ESCA 5800        (manufactured by Ulvac phi Inc.)    -   X-ray source: Mg—Kα ray    -   X-ray radiation angle: 30°

In addition, from the obtained presence ratios of the individualelements, the covering rate of the silica film in the water resistantaluminum pigment was calculated by the above formula (8). The presenceratios of the individual elements and the covering rate of the silicafilm are shown in Tables 4 and 5.

In Al (atomic percent) shown in Tables 4 and 5, as described above, Alpresent in the form of an Al element and Al present in the form of Al—Oare included. When the peaks thereof are separated from each other, theratio of Al in the form of an Al element to Al present in the form ofAl—O can be obtained. As a result, in Examples 1 to 7, Example 10,Comparative Examples 1 and 2, Comparative Examples 8 to 11, andReference Examples 1 and 2, the ratio of Al in the form of an Al elementwas 18%, and the ratio of Al in the form of Al—O was 82%. In addition,in Example 11, the ratio of Al in the form of an Al element was 20%, andthe ratio of Al in the form of Al—O was 80%.

TABLE 4 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 TYPE OF WATER RESISTANTA B-1 B-2 C D ALUMINUM PIGMENT DISPERSION XPS MEASUREMENT C 20.4 21.117.7 23.5 22.1 RESULT UNDER O 53.6 53.6 55.8 52.6 52.6 MEASUREMENT Al9.5 8.1 7.2 10.3 11.3 CONDITIONS (1) Si 16.5 17.2 19.3 13.6 14.0 (atom%) COVERING RATE (%) 69.5 72.7 78.4 61.8 60.6 EXAMPLE 5 EXAMPLE 6EXAMPLE 7 EXAMPLE 10 EXAMPLE 11 TYPE OF WATER RESISTANT E F G J KALUMINUM PIGMENT DISPERSION XPS MEASUREMENT C 19.7 20.2 19.1 15.6 13.4RESULT UNDER O 54.6 53.6 55.0 56.4 57.4 MEASUREMENT Al 8.2 7.4 7.9 12.012.7 CONDITIONS (1) Si 17.5 18.8 17.9 16.0 16.6 (atom %) COVERING RATE(%) 73.8 76.6 74.6 64.4 64.0

TABLE 5 COMPARATIVE COMPARATIVE COMPARATIVE COMPARATIVE EXAMPLE 1EXAMPLE 2 EXAMPLE 8 EXAMPLE 9 TYPE OF WATER RESISTANT L M S T ALUMINUMPIGMENT DISPERSION XPS MEASUREMENT C 27.8 18.4 18.9 22.4 RESULT UNDER O46.3 58.9 58.0 57.0 MEASUREMENT Al 23.6 17.6 18.5 16.7 CONDITIONS (1) Si2.3 5.1 4.6 3.9 (atom %) COVERING RATE (%) 27.9 26.0 22.9 16.9COMPARATIVE COMPARATIVE REFERENCE REFERENCE EXAMPLE 10 EXAMPLE 11EXAMPLE 1 EXAMPLE 2 TYPE OF WATER RESISTANT U V W X ALUMINUM PIGMENTDISPERSION XPS MEASUREMENT C 16.5 23.6 28.8 24.0 RESULT UNDER O 59.048.5 46.4 48.2 MEASUREMENT Al 19.1 22.6 19.0 21.4 CONDITIONS (1) Si 5.45.3 5.9 6.4 (atom %) COVERING RATE (%) 25.7 20.0 29.4 29.6

(2) Measurement Conditions 2

Besides the measurement performed under the “(1) measurement conditions1”, the presence ratios of C, O, Si, and Al of the surface of each ofthe aluminum pigments of the dispersions J and K were measured under thefollowing measurement conditions 2.

Measurement Conditions 2

-   -   X-ray photoelectron spectroscopic apparatus: ESCA 1000        (manufactured by Ulvac phi Inc.)    -   X-ray source: monochromatic Al—Kα ray    -   X-ray radiation angle: 15°

In addition, from the obtained presence ratios of the individualelements, the covering rate of the silica film in the water resistantaluminum pigment was calculated by the above formula (8). The presenceratios of the individual elements and the covering rate of the silicafilm are shown in Table 6.

In Example 10 shown in Table 6, the ratio of Al in the form of an Alelement was 18%, and the ratio of Al in the form of Al—O was 82%. Inaddition, in Example 11 shown in Table 6, the ratio of Al in the form ofan Al element was 16%, and the ratio of Al in the form of Al—O was 84%.

TABLE 6 EXAMPLE 10 EXAMPLE 11 TYPE OF WATER RESISTANT J K ALUMINUMPIGMENT DISPERSION XPS MEASUREMENT C 18.7 18.2 RESULT UNDER O 52.2 54.0MEASUREMENT Al 16.2 14.3 CONDITIONS (2) (atom %) Si 12.9 13.5 COVERINGRATE (%) 51.9 55.7

(3) Measurement Conditions 3

Besides the measurement performed under the above “(1) measurement 1”,in order to confirm the change of the covering rate of the silica filmwith time, a test was performed on the dispersion B-2 of Example 2 underthe following conditions.

In particular, after the dispersion B-2 of Example 2 was held at aconstant temperature of 25° C. for 140 days, the presence ratios of C,O, Si, and Al were measured by a test method performed under conditionssimilar to the above “(1) measurement conditions 1”.

In addition, from the obtained presence ratios of the individualelements, the covering rate of the silica film in the water resistantaluminum pigment was calculated by the above formula (8). The presenceratios of the individual elements and the covering rate of the silicafilm are shown in Table 7.

In Example 2 shown in Table 7, the ratio of Al in the form of an Alelement was 18%, and the ratio of Al in the form of Al—O was 82%.

TABLE 7 EXAMPLE 2 TYPE OF WATER B-2 RESISTANT ALUMINUM PIGMENTDISPERSION XPS MEASUREMENT C 24.5 RESULT UNDER O 51.3 MEASUREMENT Al 5.7CONDITIONS (3) Si 18.5 (atom %) COVERING RATE (%) 81.1

4.25.5 Observation by SEM and TEM

(1) Observation by SEM

After the dispersion A was dripped/applied to printing paper (PM photopaper (gloss) model No. KA450PSK, manufactured by Seiko EpsonCorporation), drying was performed at room temperature for 1 day. Thesurface condition of the sample thus obtained was observed by a SEM(S-4700 manufactured by Hitachi High-Technologies Corporation). The SEMimage is shown in FIG. 2.

(2) Observation by TEM

The cross-sectional condition of the sample obtained by the above“4.25.5(1)” was observed using a transmission electron microscopeTecnaiG2f30 (manufactured by Philips Company, hereinafter referred to as“TEM”). The TEM images are shown in FIGS. 3 to 5.

4.25.6 Evaluation of Degree of Gloss of Aqueous Ink Composition

(1) Preparation of Aqueous Ink Composition (Example 12 and ReferenceExample 3)

In order to obtain the composition shown in Table 8, after ion exchangewater was added to 58.8 parts by mass of the dispersion A prepared inthe above “4.1 Example 1”, 10 parts by mass of glycerin, 5 parts by massof trimethylolpropane, 1 part by mass of 1,2-hexanediol, 1 part by massof Olfin E1010 (acetylene glycol-based surfactant, manufactured byNisshin Chemical Co., Ltd.), and 1 part by mass of triethanolamine sothat the total mass was 100 parts by mass, mixing and stirring were thencarried out. Accordingly, an aqueous ink composition A of Example 12containing 1 mass percent of the aluminum pigment was obtained.

In addition, except that in the preparation of the above aqueous inkcomposition A, 20 parts by mass of the dispersion W was added instead ofthe dispersion A, an aqueous ink composition W of Reference Example 3containing 1 mass percent of the aluminum pigment was obtained in amanner similar to that described above.

(2) Formation of Evaluation Sample

As an exclusive cartridge of an ink jet printer PX-G930 (manufactured bySeiko Epson Corporation), an ink cartridge filled with the above aqueousink composition was formed. Next, the obtained ink cartridge was fittedto a black line of the ink jet printer PX-G930, and commerciallyavailable ink cartridges were fitted to the other nozzle lines. Sincethe commercially available ink cartridges fitted to the lines other thanthe black line were each used as a dummy and were not used for theevaluation in this example, the effects of the invention were notinfluenced thereby.

Next, by using the above printer, the aqueous ink composition fitted tothe black line was ejected to photo paper <gloss> (manufactured by SeikoEpson Corporation), so that a recording material on which a solidpattern image was printed was obtained. As the printing conditions, anejected ink weight per one dot was set to 20 ng, and the resolution wasset to 720 dpi by 720 dpi.

(3) Evaluation Method of Image

The degree of gloss at 60° of the obtained image was measured by a glossmeter, MULTI Gloss 268 (manufactured by Konica Minolta Co., Ltd.). Theevaluation criteria of the degree of gloss of the obtained image are asfollows. The results of the evaluation test of the degree of gloss areshown in Table 8.

-   “A”: Degree of gloss of 300 or more (clear metallic gloss)-   “B”: Degree of gloss of 250 to less than 300 (matte metallic gloss)-   “C”: Degree of gloss of 200 to less than 250 (no metallic gloss)-   “D”: Measurement not available (ejection of aqueous ink composition    being not available)

TABLE 8 EXAMPLE 12 REFERENCE EXAMPLE 3 TYPE OF AQUEOUS INK COMPOSITION AW ALUMINUM PIGMENT CONCENTRATION IN AQUEOUS 1 1 INK COMPOSITION (MASSPERCENT) WATER RESISTANT ALUMINUM TYPE A W PIGMENT DISPERSION ADDITIONAMOUNT (MASS 58.8 20 PERCENT) POLYALCOHOL TYPE GLYCERIN GLYCERINADDITION AMOUNT (MASS 10 10 PERCENT) TYPE TRIMETHYLOLPROPANETRIMETHYLOLPROPANE ADDITION AMOUNT (MASS 5 5 PERCENT) ALKANEDIOL TYPE1,2-HEXANEDIOL 1,2-HEXANEDIOL ADDITION AMOUNT (MASS 0.67 0.67 PERCENT)SURFACTANT TYPE OLFIN E1010 OLFIN E1010 ADDITION AMOUNT (MASS 1 1PERCENT) pH ADJUSTER TYPE TRIETHANOLAMINE TRIETHANOLAMINE ADDITIONAMOUNT (MASS 1 1 PERCENT) ION EXCHANGE WATER BALANCE BALANCE EVALUATIONRESULT DEGREE OF GLOSS 307 NOT EJECTED EVALUATION OF DEGREE OF A D GLOSS

4.25.7 Evaluation Results (1) Examples 1 to 12

In each of the dispersions A to K of Examples 1 to 11, the waterresistant aluminum pigment which was the aluminum pigment covered withthe silica film was dispersed in an aqueous solution containing at leastone of the copolymers A, B, and C. Accordingly, as shown in Table 1, theresults of the water resistant evaluation test, the dispersibilityevaluation test, and the gloss evaluation test were superior, and asuperior water resistant aluminum pigment dispersion could be obtained.

Among those mentioned above, it was confirmed that the dispersibility ofeach of the dispersions B-1 and B-2 of Example 2, the dispersion H ofExample 8, the dispersion J of Example 10, and the dispersion K ofExample 11 was significantly superior.

As shown in Table 4, in each of the dispersions A to G of Examples 1 to7 and the dispersions J and K of Examples 10 and 11, the covering rateof the silica film was 30% or more. Since the dispersions A to G ofExamples 1 to 7 and the dispersions J and K of Examples 10 and 11 eachhad superior water resistance, dispersibility, and gloss, it wassuggested that when the covering rate of the silica film was 30% ormore, the surface of the aluminum pigment was sufficiently covered withthe silica film, and a superior silica film was formed.

In addition, as shown in Tables 4 and 7, it was confirmed that even when140 days passed, the covering rate in the dispersion B-2 of Example 2was equivalent to that immediately after the aluminum pigment wasdispersed. Hence, it was shown that in the dispersion B-2 of Example 2,a superior silica film was formed on the surface of the aluminumpigment, the dispersibility thereof was superior, and the waterresistance of the aluminum pigment contained in the dispersion B-2 wassuperior.

FIG. 2 is a SEM image showing the surface condition of a sample formedusing the dispersion A of Example 1. Accordingly, it was confirmed thatplate-shaped particles of the aluminum pigment were disposed on arecording medium so as to be overlapped with each other. In addition,FIG. 3 is a TEM image showing the cross-sectional condition of thesample formed using the dispersion A of Example 1, and it was confirmedthat the particles of the aluminum pigment were disposed so as to beoverlapped with each other.

FIG. 4 is an enlarged TEM image of the portion a shown in FIG. 3. Asshown in FIG. 4, it was confirmed that in one flat-shaped aluminumpigment particle, the surface thereof was covered with a silica layerhaving a thickness of approximately 4.5 nm. Accordingly, it was shownthat the aluminum pigment was sufficiently protected by the silicacovering film, and that the water resistance was imparted thereby.

In addition, from FIG. 4, it was confirmed that between the aluminumlayer and the silica layer, a layer having a thickness of approximately4.5 nm and containing aluminum oxide was formed. It is believed thatthis layer containing aluminum oxide was generated after the hydrolysisreaction occurred between TEOS and a hydroxyl group present on thesurface of the aluminum pigment and was derived from a hydroxyl groupwhich was present on the surface of the aluminum pigment and which wasnot allowed to react with TEOS.

In addition, FIG. 5 is a TEM image showing the cross-sectional conditionof the sample formed using the dispersion A of Example 1. As shown by bin FIG. 5, it was confirmed that at the end portion of the aluminumpigment, the silica film was also preferably formed. Accordingly, it wasshown that the surface of the aluminum pigment was sufficientlyprotected by the silica film and that the water resistance of thealuminum pigment was improved by the silica film.

As shown in Table 8, it was shown by the result of the evaluation testof the degree of gloss that the aqueous ink composition A of Example 12prepared by using the dispersion A of Example 1 had a superior metallicgloss. Accordingly, it was shown that the dispersion A of Example 1 canbe preferably used for an ink jet recording apparatus.

(2) Comparative Examples 1 to 11, and Reference Examples 1 to 3

Since the step of adding TEOS was not performed for the dispersion L ofComparative Example 1, in the water resistance evaluation test, thewater resistance was markedly inferior.

The dispersion M of Comparative Example 2 and the dispersion S ofComparative Example 8 did not contain the copolymers A, B, and C in theaqueous solvents. Hence, agglomeration occurred in the dispersibilityevaluation test, and in addition, also in the gloss evaluation test, thegloss of the coating film could not be obtained.

The dispersions N to R of Comparative Examples 3 to 7 did not containthe copolymers A, B, and C in the aqueous solvents and containedsurfactants other than those mentioned above. Hence, in thedispersibility evaluation test, agglomeration occurred, and in addition,in the gloss evaluation test, the gloss of the coating film could not beobtained.

The dispersion T of Comparative Example 9 did not contain the copolymersA, B, and C in the aqueous solvent and contained diethylamine as a basecatalyst. As a result, since agglomeration markedly occurred, the waterresistance evaluation test and the gloss evaluation test were stopped.

The dispersion U of Comparative Example 10 did not contain thecopolymers A, B, and C in the aqueous solvent and also did not use TEOSas a silica raw material. As a result, the water resistance was notsuperior.

The dispersion V of Comparative Example 11 did not contain thecopolymers A, B, and C in the aqueous solvent and also did not use TEOSas a silica raw material. Hence, in the dispersibility evaluation test,agglomeration occurred, and in addition, in the gloss evaluation test,the gloss of the coating film could not be obtained.

The dispersion W of Reference Example 1 and the dispersion X ofReference Example 2 were not superior in dispersibility and gloss of thecoating film. Hence, it was shown that when the pre-addition ofsurfactant was performed, the dispersibility of the water resistantaluminum pigment dispersion and the gloss of the coating film weredegraded.

In addition, as shown in Table 8, the aqueous ink composition W ofReference Example 3 prepared using the dispersion W of Reference Example1 could not be ejected from the ink jet recording apparatus, and thedegree of gloss could not be measured. Hence, it was shown that thedispersion W of Reference Example 1 was difficult to use for an ink jetrecording apparatus.

The invention is not limited to the embodiments described above and maybe variously modified and changed within the scope of the invention. Forexample, the invention may include configurations substantially the sameas the configurations described in the embodiments (for example, aconfiguration having the same function, method, and result or aconfiguration having the same object and advantage). In addition, theinvention may include configurations in which unessential portions inthe configurations described in the embodiments are replaced withothers. Also, the invention may include configurations that have thesame operations and effects or configurations that achieve the sameobjects as the configurations described in the embodiments. Furthermore,the invention may include configurations that have known techniquesadded to the configurations described in the embodiments.

What is claimed is:
 1. An ink composition comprising a water resistantaluminum pigment and water, wherein the water resistant aluminum pigmentis formed of an aluminum pigment having an average thickness from 5 nmto 30 nm and a covering film which contains Si and is formed on thesurface of the aluminum pigment; and wherein the coverage ratio of thesurface of the aluminum pigment by the covering film, calculated fromthe composition ratio of C, O, Al, and Si detected by XPS measurement atan incident angle of 30°, is in a range from 30% to 90%.
 2. The inkcomposition according to claim 1, wherein the covering film has athickness from 0.5 nm to 10 nm.
 3. The ink composition according toclaim 1, wherein the aluminum pigment is plate-shaped aluminumparticles.
 4. The ink composition according to claim 1, wherein thealuminum pigment has a 50% average particle diameter from 0.5 μm to 3μm.
 5. The ink composition according to claim 1, wherein the coveringfilm has a thickness from 1 to 9 nm.
 6. The ink composition according toclaim 1, wherein the coverage ratio is in a range of 50% to 90%.
 7. Theink composition according to claim 6, wherein the covering film has athickness from 1 to 9 nm.
 8. The ink composition according to claim 7,wherein the coverage ratio is at least 60.6%.